. Project Summary/Abstract AIDS continues to be an expanding pandemic. The successful development of a safe and effective HIV vaccine is a global health priority that has been hampered by our current inability to deliver HIV antigens efficiently to the immune system to prime predictable, high frequency, and durable immune responses in humans. To approach this problem, we propose a unique prime-boost vaccine strategy that pairs two live mucosal vectors, Listeria monocytogenes (Listeria, Lm) and adenovirus (Ad), each of which has been tested in clinical trials in humans, and both have shown the ability in small animal models and NHP to elicit strong cellular immunity. The proposal is provoked by our recent observations that mucosal administration of attenuated Listeria followed by a boost by replication-incompetent Ad5 elicited potent peripheral and mucosal T cell responses, and by the development of new Ad variants that circumvent anti-Ad5 immunity. Because most HIV infections result from heterosexual transmission to women, and because the virus targets lymphocytes in the gut and vaginal mucosae for rapid elimination, this project aims by use of these vectors to strengthen immunity and protection at these important mucosal sites. The laboratories of Drs. Dan Barouch at Beth Isreal Deaconess Medical Center and Fred Frankel at the University of Pennsylvania School of Medicine will collaborate to explore the potential synergy of these two vectors. Dr. Frankel will examine vector interactions in mice, while Dr. Barouch will conduct concurrent pilot studies testing these vectors in the nonhuman primate model.